1. Field of the Invention
The present invention relates to current supply means for series-fed electronic circuits, and in particular to such circuits having a Zener diode connected between the terminals for the feed current together with a rectifying diode and a charging capacitor, the electronic circuit being connected to a consumer.
2. Description of the Prior Art
Intermediate regenerative amplifiers (sometimes called repeaters or regenerators) are included at predetermined intervals along lines for the transmission of digital signals to a consumer. The intermediate amplifiers are generally supplied with a voltage in a series-feed arrangement. A constant current of approximately 50 mA is fed-in from a transmitting station, generally through the center tap of a transformer, and forms a loop so as to return to the transmitting station via the return data connection. A constant voltage is obtained in conventional devices for the supply votage for the intermediate amplifiers by means of a Zener diode, a rectifying diode, and a charging capacitor.
A current supply arrangement of this type is described in N.T.C. 1977, pages 44:1-1 to 1-4. This publication also describes problems caused by interference voltages. In order to minimize the effects of such interference voltages, the capacitance of the charging capacitor is selected to be as high as possible. Should the supply current temporarily be absent, the rectifying diode is disconnected and the circuit arrangement is supplied by means of the charging capacitor.
Currents of less than 5 mA effective at approximately 16 Hz represent common disturbances to the feed current. In some situations, however, current fluctuations of as much as 50 mA may effectively occur. Disturbances of 10 A at 50 Hz also may occur temporarily; in the event of lightening strikes current peaks of up to 100 A have been measured for a duration of 1 ms.
Such disturbances manifest themselves, for example, in the intermediate amplifiers by amplitude modulation and phase modulation (jitter) of the transmitted data.